Leptoplax doederleini ( Thiele, 1909 )

Sirenko, Boris I. & Saito, Hiroshi, 2017, New species of chitons of the superfamily Cryptoplacoidea (Mollusca: Polyplacophora) from Vietnamese waters, Zootaxa 4299 (4), pp. 451-506 : 460-463

Leptoplax doederleini ( Thiele, 1909)

Figs 9–12 , 43 D

Notoplax döderleini Thiele, 1909: 39 , pl. 5, figs 32–38; Kaas & Van Belle, 1980: 40; 1998: 64. Notoplax (Notoplax) doederleini: Van Belle, 1980: 478 –480, fig. 4.

“ Notoplax ” doederleini: Saito, 1998: 160 , fig. 2N; 2000a: 102.

Leptoplax doederleini: Saito, 2000b: 21 , pl. 10, fig. 6; 2001: 200, fig. 14; 2006a: 217.

Type material. Holotype, ZMB Moll. 102017.

Type locality. Kajiyama (=? Katsuyama, Tokyo Bay), Japan.

Material examined. Southern Vietnam, Nha Trang Bay, Dat Id., 13°41.410´N, 109°13.577´E, 0–0.4 m, under stones, 2 spms ( ZISP 2237, 2238 ), BL 15 & 17 mm, 25.04.2013, leg. B. Sirenko.

Description. Animal medium in size, elongate-oval, moderately elevated. Color of tegmentum pinkish white, maculated with white, olive green, dark pink and dark brown; hind margins of intermediate valves with regular dark brown blotches; jugum tinted with olive green bounded by white lines. Girdle beige with pale reddish brown bands.

Head valve semicircular, posterior margin widely V-shaped; anterior slope slightly convex; no radial ribs. Intermediate valve roughly trapezoidal or lunate in outline, moderately elevated, subcarinate, beaked; front margin straight between apophyses; hind margin concave at both sides of beak; side slope nearly straight; jugum wedgeshaped, smooth on surface, wavy in side margins; lateral area ambiguously separable from pleural area by weak angulation on diagonal line. Tail valve elliptical in outline with central mucro; width of tegmentum only slightly narrower than head valve; posterior slope slightly concave.

Pustules on tegmentum arranged basically in quincunx order on head valve, lateral areas of intermediate valves and posterior area of tail valve, somewhat irregular in pleural areas and antemucronal area. Each pustule elongate oval, flat at top with 2–3 aesthete pores and several aesthete pores on prepustular slope. All aesthete pores on pustules of almost uniform size, approximately 12 µm x 7 µm, hardly distinguishable macr- and micraesthete pores. Micraesthete pores present on tegmental plain.

Articulamentum well developed, rather thin, white. Apophyses widely separated; anterior margin gently round in intermediate valves, concave in tail valve. Insertion plates long, striated on outer surface. Slits narrow. Slit formula 5/1/8.

Girdle rather wide, 2.5 mm at side of valve V. Dorsal side of girdle with three types of spicules or needles: Smallest spicules slender, smooth, sharply pointed at tip, 35 µm x 8 µm; among these minute spicules, long, slender, smooth, slightly curved spicules, 45–80 µm x 8–12 µm and thick, curved, smooth or longitudinally angulated, sharply pointed needles, 80–120 µm x 15 µm, which are more or less oblong in cross section implanted. Sutural tufts small, of up to 13 long needles, 278–660 µm x 27–35 µm. Marginal needles smooth, slightly curved, attaining 346 µm x 25 µm. Ventral spicules flat, 18–110 µm x 8–20 µm; ventral spicules near girdle margin occasionally with several riblets.

Gills extending from valve VII to valve V, composed of 13 ctenidia on each side.

Radula 4.1 mm in length with 40 rows of mature teeth. Central tooth narrow, spatula-shaped with weakly bilobed blade, keeled at basal portion. First lateral (centro-lateral) tooth with slightly thickened, weakly produced antero-dorsal corner. Major lateral tooth tricuspid; denticles tips blunt, central one slightly longer than others.

Distribution. From Pacific coast of central Japan to Okinawa, Hong Kong and northern Vietnam, 0– 20 m.

Remarks. Leptoplax doederleini resembles Leptoplax coarctata (Sowerby, 1841) in general shape of the valves and the dorsal side of the girdle with three types of spicules or needles, but they are distinguishable by the following features: The valves of the former are wider than those of latter; the pustules on the tegmentum which have 2–3 aesthete pores on each pustule in the former whereas only one in the latter; curved spicules of the dorsal side of the girdle which are smooth or occasionally angulated in the former, while sculptured with irregular transverse, screw-like ridges in the latter.

This is the first record of this species from Vietnam.

Figures

FIGURE 9. Leptoplax doederleini, Vietnam, Hon Dat, Cat Ba Id., BL 15 mm: A. Valve I, dorsal view; B. Valve V, dorsal view; C. Valve VIII, dorsal view; D. Half of valve IV, ventral view; E. Valve V, detail of tegmentum in jugal and lateropleural areas; F. Valve VIII, lateral view. G. Valve V, rostral view.

FIGURE 10. Leptoplax doederleini, Vietnam, Hon Dat, Cat Ba Id., BL 15 mm: A, B. Valve V, detail of tegmentum in jugal and lateropleural areas.

FIGURE 11. Leptoplax doederleini, Vietnam, Hon Dat, Cat Ba Id., BL 15 mm: A. Dorsal spicules and needles, marginal needles and ventral spicules; B. Dorsal spicules; C. Tuft and dorsal spicules; D. Radula.

FIGURE 12. Leptoplax doederleini, Vietnam, Hon Dat, Cat Ba Id., BL 15 mm: A. Needles of tufts; B. Dorsal spicules and needles; C. Marginal needles, D. Ventral spicules; E. Head of major lateral tooth of radula; F. Central and first lateral teeth of radula; G. Pustule of lateropleural areas of tegmentum with aesthete pores. Scale bars: 100 µm.

FIGURE 43. Images of species of genera Notoplax and Leptoplax: A. Notoplax conica, Southern Vietnam, Nha Trang Bay, Tre Id, BL 10 mm; B. Notoplax odysseyi n. sp., Southern Vietnam, Off Phan Rang, 95 m, on old corals, holotype, BL 51 mm; C. Leptoplax nhatrangi n. sp., Nha Trang Bay, Dat Id., 7 – 12 m, on shells of Malleus malleus, holotype, BL 5.2 mm; D. Leptoplax doederleini, Vietnam, Nha Trang Bay, Dat Id., intertidal, under stones, BL 15 mm; E. Leptoplax tongkingi n. sp., Gulf of Tongking, Cat Ba Id., 3 – 4 m, on shells, paratype, BL 5 mm.